rust-cpython: require GIL to borrow immutable reference from PySharedRefCell
Since the inner value may be leaked, we probably need GIL to guarantee that
there's no data race.
inner(py).borrow() is replaced with inner_shared(py).borrow(), which basically
means any PySharedRefCell data should be accessed through PySharedRef wrapper.
# name space package to host third party extensions
from __future__ import absolute_import
import pkgutil
__path__ = pkgutil.extend_path(__path__, __name__)